流态化制备纳米碳化钨机理及传递-反应耦合规律

Ultrafine/nano crystalline WC-Co is the key development direction of cemented carbide because of its high hardness and high strength. The preparation of nano-sized WC powder is the premise and key. However, the slow rate of mass transfer diffusion of carbon to tungsten lattice and the nucleation rate of WC are the key problems that restrict the preparation of nano-sized WC..To solve the problem, this application makes full use of the advantages of fluidized bed reactor and chemical vapor transport (CVT) reaction characteristics of tungsten oxide, and puts forward a new idea of tungsten oxide chemical vapor transport reaction and reduction-carbonization via fluidization. Tungsten oxide is used as the raw material to generate gaseous tungsten source via CVT reaction with gaseous chemical transfer medium in a bubbling fluidized bed reactor. Then, gaseous tungsten source homogeneously reacts with reduction-carbonated gases and can be rapidly nucleated to prepare nano-sized WC. .The main contents and objectives of this project are as follows：investigating the CVT reaction process of tungsten oxide, and establishing the rate control mechanism of gasification reaction; investigating the coupling process of reduction-carbonization and CVT reaction, analyzing the change rule of phase, structure, and carbon species during the reaction process, revealing the preparation mechanism of nano-sized WC, and establishing the control mechanism of preparation process; analyzing the process of transfer-reaction coupling between the reaction mediums in the reactor by using fluid simulation soft ware, and establishing the reaction kinetics equation, accordingly, guiding the preparation process of nano-sized WC..The completion of this application will lay a theoretical foundation for the preparation of nano-sized tungsten carbide in homogeneous gas phase and the development of the application of fluidization technology.

超细/纳米晶WC-Co具有高硬度和高强度而成为硬质合金的重点发展方向，而纳米WC粉的制备则是前提和关键，但碳向钨晶格的固相传质扩散和形核速率慢是制约纳米WC制备的关键问题。本项目结合流化床反应器的优势和钨氧化物具有化学蒸汽转移（CVT）反应的特性，提出钨氧化物流态化化学蒸汽转移-气态均相还原碳化的新思路。以钨氧化物为原料，在流化床反应器内与转移介质发生CVT反应生成气态钨源，再与碳化气通过均相反应快速形核制备纳米WC。通过考察钨氧化物CVT反应过程规律，建立其反应速率调控机制；考察还原碳化与CVT反应的耦合过程，分析反应过程物相、结构、碳物种变化规律，揭示纳米WC制备过程机理，建立其制备过程调控机制；采用Fluent软件模拟分析反应器内反应介质间的传递-反应耦合过程，建立其反应动理学方程，指导纳米WC制备过程调控。本项目的完成将为气相均相制备纳米碳化钨，及拓展流态化技术的应用奠定理论基础。

超细/纳米晶WC-Co具有高硬度和高强度而成为硬质合金的重点发展方向，而纳米WC粉的制备则是前提和关键。本项目以WO2.72为原料，采用流化床为反应器，强化其制备过程。建立了WO2.72还原过程调控机制及其还原动力学方程，也建立了其碳化过程调控机制，获得了满足国标的纳米碳化钨粉体；厘清了氧化钨流态化制备超细碳化钨的反应路径和过程机理；阐明了流化床内氧化钨在还原碳化过程中物质的传递-反应耦合过程规律，建立了碳化钨生成速率曲线。本项目显著强化了纳米碳化钨制备过程，比传统制备技术温度降低约350～450℃条件下制备出BET粒径约为46nm的纳米级碳化钨粉体。同时，还厘清了各要素的耦合作用机制，实现了对WC制备过程的精确调控，可为进一步放大提供工艺技术和理论依据。